1. Field of the Invention
The present invention relates to a light-emitting unit. Particularly it relates to a light-emitting unit constituted by a combination of a light-emitting device and a fluorescent material.
The present application is based on Japanese Patent Application No. 2000-258090, which is incorporated herein by reference.
2. Description of the Related Art
There has been developed a light-emitting unit in which apart of light emitted from a light-emitting device is subjected to wavelength conversion by a fluorescent material and the part of light which has been subjected to wavelength conversion is mixed with the other part of the light which has not been subjected to wavelength conversion to thereby emit light with an emission light color different from that of the light emitted from the light-emitting device.
For example, a light-emitting unit using a group III nitride compound semiconductor light-emitting device as a light-emitting device for emitting blue light and using an yttrium-aluminum-garnet fluorescent material (YAG) activated with cerium (Ce) as a fluorescent material has been put on the market. In such a light-emitting unit, for example, a cup portion of a lead frame in which a light-emitting device is mounted is filled with a light-transmissible material containing a dispersed fluorescent material (YAG) to thereby form a fluorescent layer in the light-emitting direction of the light-emitting device. In such a configuration, when the light emitted from the light-emitting device passes through the fluorescent layer, a part of the light is radiated after the part of light is absorbed by the fluorescent material (YAG) or the wavelength of the part of light is converted by the fluorescent material. The other part of light is radiated after transmitted through the fluorescent layer without being absorbed by the fluorescent material. As a result, the two kinds of light are mixed with each other to thereby obtain emission of white light.